1. Field of the Invention
This invention relates in general to the conveyance of hydrocarbons from a subsea well or wells, and in particular to an apparatus and assembly, and methods associated therewith, for a pipeline end terminal and foundation assembly for a subsea pipeline.
2. Background of the Invention
When conveying hydrocarbons from a subsea well, the hydrocarbons are often communicated through a flowline extending along the surface of the sea floor. The flowline extends from a single subsea wellhead, from subsea processing equipment, or from a subsea collection manifold.
The flowline or pipeline often expands and contracts due to the heat emitted from the flow of hot hydrocarbons passing through the flowline. The flowline contracts when the flow of the hydrocarbons is stopped. The flowline is also in the contracted state when it is initially installed. Therefore, during operations, the flowline expands to a state that is not experienced during installation and workover operations.
The expansion includes both a radial expansion of the pipeline, as well as a longitudinal expansion of the pipeline. When both of the pipeline ends are secured to fixed locations, such longitudinal expansion causes the middle portion of the pipeline to buckle and drift from its installed position, as well as exerting large forces on the structures at the ends of the pipeline. Such buckling and drift can damage the integrity of the pipeline, as well as the equipment associated with the ends of the pipeline. The expansion is even more significant, and creates larger forces, when the pipeline is extending along the sea floor for deep operations because the pressure and temperature of the surrounding deep water is more extreme than in shallower operations.
In previous assemblies, both ends of the pipeline have been secured to the sea floor, but this results in the problems discussed above. In other assemblies, only one end of the pipeline was secured to the sea floor while the other end was either free to move or was tethered to a foundation structure. Such assemblies alleviated much of the stress forces at the ends of the pipeline, but the end that is not secured tended to drift over a wide range due to the thermal expansion of the pipeline. Such drift makes it difficult for workover operations and for connection of the end of the flowline with other subsea equipment.